Optical pickup

ABSTRACT

An optical pickup comprises an objective-lens driving device including a movable section provided with an objective lens, a focusing coil, and tracking coils, and a fixed section provided with a single magnetic circuit having a magnetic gap, the focusing coil and the tracking coils being disposed in the magnetic gap. The point of application of a tracking-driving force, the point of application of a result force of focusing-driving forces occurring in and outside the magnetic gap, and the position of the center of gravity of the movable section are made to substantially coincide with each other. In addition, the objective lens and the magnetic circuit are disposed within an area of a window in a lower shell of a optical disk. Further, a through hole for accommodating a lower portion of a yoke of the magnetic circuit is provided in a mounting base on which the objective-lens driving device is mounted. An inclining fulcrum and a height adjusting means for inclining the objective-lens driving device about the inclining fulcrum are provided in the vicinities of the through hole.

This application is a continuation of Ser. No. 08/994,560 filed Dec. 19,1997 now U.S. Pat. No. 6,084,834, which is a continuation of Ser. No.08/888,232, filed Jul. 3, 1997 now U.S. Pat. No. 5,877,904, which is adivision of Ser. No. 08/813,314, filed Mar. 10, 1997 abandoned, and adivision of Ser. No. 08/810,340 filed Feb. 27, 1997 U.S. Pat. No.5,724,337, which is a continuation of Ser. No. 08/330,671 filed Oct. 28,1994 abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical pickup for recording andreproducing information with respect to an optical disk. Moreparticularly, the present invention relates to an objective-lens drivingdevice and a mechanism for adjusting the inclination of an objectivelens which are aimed at making the optical pickup compact and thin andstabilizing the driving of the objective lens in both a focusingdirection and a tracking direction.

2. Description of the Related Art

In general, an optical pickup is comprised of an objective-lens drivingdevice having an objective lens and an optical system block fortransmitting and receiving light with respect to the objective lens, andis structured such that the objective-lens driving device is mounted ona mounting base of the optical system block.

To accurately effect the recording and reproduction of information withrespect to an optical disk, it is necessary to accurately set theoptical axis of the objective lens perpendicular to the disk surface.

For this reason, a mechanism for adjusting the inclination of anobjective lens is conventionally known (e.g., Unexamined Japanese PatentApplication (Kokai) No. 62-287443) which is arranged as follows: Asshown in FIG. 1, a spherically convex mounting surface 103 is made toproject from a bottom surface 102 a of an objective-lens driving device102 having an objective lens 101. In addition, as shown in FIG. 2, aspherically concave mounting surface 106 is formed in a mounting base105 of an optical system block 104, the spherically convex mountingsurface 103 is fitted in the spherically concave mounting surface 106,and the inclination of the objective lens 101 is made adjustable withrespect to the center (fulcrum) 107 of a sphere formed by thespherically convex mounting surface 103 and the spherically concavemounting surface 106 by means of height adjusting screws 108.

However, since the spherically convex mounting surface 103, thespherically concave mounting surface 106, and the height-adjustingscrews 108 are disposed between the objective-lens driving device 102and the mounting base 105 of the optical system block 104, thethicknesswise dimension becomes large, thereby constituting a hindranceto the attempt to make the optical pickup thin.

In addition, to accurately effect the recording and reproduction ofinformation with respect to an optical disk, it is necessary to preventthe occurrence of unwanted resonance. To prevent the occurrence of suchunwanted resonance, in a conventional objective-lens driving device 201Ashown in the perspective view in FIG. 3, the position of the center ofgravity of a movable section 204, which has an objective lens 202, afocusing coil 203A for a focusing direction Z, and a pair of trackingcoils 203B for a tracking direction Y, is aligned with an optical axis205, and the central axes of the focusing coil 203A and the trackingcoils 203B are aligned with the optical axis 205 (e.g., UnexaminedJapanese Patent Application (Kokai) No. 2-230522).

The optical pickup having this arrangement is capable of preventing theoccurrence of unwanted resonance, but it is necessary to dispose a lightsource, a reflecting mirror, a light-receiving element, and the likebelow the objective-lens driving device to effect the recording andreproduction of information. Hence, it has been difficult to make theoptical pickup compact and thin.

To make the objective-lens driving device compact and thin, in aconventional objective-lens driving device 201B shown in the explodedperspective view in FIG. 4, the central axes of a focusing coil 208A anda pair of tracking coils 208B are not aligned with the optical axis 205,and the focusing coil 208A and the tracking coils 208B are disposed in amagnetic gap 207 provided in a single magnetic circuit 206 (e.g.,Unexamined Japanese Patent Application (Kokai) Nos. 4-102235 and4-103038).

In addition, in the objective-lens driving device disclosed inUnexamined Japanese Patent Application (Kokai) 4-103038, to accuratelydrive the movable section in the direction of the optical axis (focusingdirection), a focusing-driving force which is provided outside themagnetic gap is minimized, so as to prevent an unnecessary force, suchas moment, from acting in the movable section. It has been thought thatthis focusing-driving force occurring outside the magnetic gap, i.e.,the leakage flux density, should be suppressed to as low a level aspossible partly for preventing interference with metallic parts such asa motor disposed in the vicinity of the objective-lens driving device.

In addition, although the conventional objective-lens driving device201B shown in FIG. 4 is capable of making the optical pickup compact andthin, there is a drawback in that, if an attempt is made to adjust theposition of the center of gravity to either one of the driving points,the other driving point is offset from the position of the center ofgravity, so that unwanted resonance occurs on the offset side.

FIG. 5A shows a schematic arrangement of an optical disk apparatusportion in a magneto-optic recording/reproducing system, in which anoptical disk 301 is provided with an optical pickup 304 having amagnetic head 302 on one side and an objective lens 303 on the otherside. The magnetic head 302 and the optical pickup 304 are driven in theradial direction of the optical disk 301 by a head driving device 305and a feed motor 306, respectively, and the optical disk 301 is rotatedby a spindle motor 307. Among such optical disk apparatuses, those of atype in which the optical disk 301 is covered with a cartridge 308 forthe purpose of protecting the optical disk 301 have come to be marketedin recent years. This cartridge-type optical disk is arranged asfollows: As shown in FIG. 5B, the optical disk 301 is rotatablyaccommodated in a space formed between an upper shell 308 a and a lowershell 308 b, and the shells 308 a and 308 b are provided with windows308 c and 308 d, respectively. When the optical disk 301 is not in use,the windows 308 c and 308 d are closed by a shutter 308 e, and, duringrecording or reproduction, the shutter 308 e is moved laterally to openthe windows 308 c and 308 d and insert the magnetic head 302 and theobjective lens 303 into the windows.

In the conventional optical pickup 304, as described in, for example,Unexamined Japanese Patent Application (Kokai) 61-139945, a circuit fordriving the objective lens 303 in the focusing direction and thetracking direction is disposed at a position other than that below theobjective lens 303, whereby a free space is formed below the objectivelens 303, and a reflecting mirror is disposed at that position, therebymaking the overall optical pickup 304 thin.

With such a conventional apparatus, as shown in FIG. 6A, the opticaldisk 301 and the objective lens 303 are opposed to each other with aninterval L₃₃ therebetween so that the optical axis of the objective lens303 aligns with a central portion, as viewed in the rotating directionof the disk, of the window 308 d of the lower shell 308 b. In thisarrangement, however, since a magnetic circuit 309 for effecting thepositional adjustment of the objective lens 303 in the focusing andtracking directions is disposed outside the window 308 d, there arises aneed to provide a gap L₃₁ between a lower surface of the lower shell 308b and an upper surface of a yoke 310 constituting the magnetic circuit309. As a result, the distance L₃₂ between the lower surface of thelower shell 308 b and the lower surface of the magnetic circuit 309becomes large, thereby constituting a hindrance to making the opticalpickup 304 thin and compact.

FIG. 7 shows an exploded perspective view of a conventionalobjective-lens driving device (Unexamined Japanese Patent Application(Kokai) No. 3-212826).

A conventional objective-lens driving device 401 shown in the drawing isarranged as follows: A lens holder 403 with an objective lens 402affixed thereto is cantilevered by being soldered onto a printed circuitboard 409 in which four wires 404 inserted in an intermediate member 405are secured to the intermediate member 405. The intermediate member 405is mounted on a yoke base 406.

Incidentally, the printed circuit board 409 and the four wires 404 areelectrically connected to each other. Electric current is allowed toflow across a focusing coil 407A and a pair of tracking coils 407B,which are arranged in the holder 403, via these four wires 404, tothereby drive the objective lens 402 in the focusing direction Z and thetracking direction Y.

To accurately effect the recording and reproduction of information withrespect to the optical disk, it is necessary to prevent the occurrenceof unwanted resonance.

For this reason, as shown in FIG. 8, a damping-member accommodatingportion 405 a is formed in the intermediate member 405, and a geldamping member 408 is filled in the accommodating portion 405 a.

However, as for the conventional objective-lens driving device 401,since the intermediate member 405 is attached to the yoke base 406, anda printed circuit board 409 is secured to the intermediate member 405 bymeans of screws or the like, the number of component parts used islarge. Hence, there has been a problem in that if the respectivecomponent parts are fixed by means of an adhesive, the number ofassembling steps increases, so that the fabrication is not facilitated.

In addition, if the printed circuit board 409 is secured to theintermediate member 405 by means of screws, there have been cases whereboth ends of the printed circuit board 409 at portions remote from thewires 404 become lifted off due to changes in temperature and ageddeterioration, as shown in FIG. 9. Hence, the four wires 404 arerespectively deflected or conversely pulled, and the supporting balancebecomes deteriorated, thereby resulting in changes in the angle of theoptical axis of the objective lens 402 and unwanted resonance. Further,in cases where the yoke base 406 and the intermediate member 405, andthe intermediate member 405 and the printed circuit board 409 aresecured separately, if the bottom surface of the yoke base 406 is set asan assembling reference plane A, as shown in FIG. 10, there has been aproblem in that it is difficult to set a B surface of the printedcircuit board 409 perpendicular to the reference plane A, thereby makingit impossible to drive the objective lens 402 with high accuracy.

SUMMARY OF THE INVENTION

The present invention has been devised in view of the above-describedcircumstances, and it is an object of the present invention to provide amechanism for adjusting the inclination of an objective lens which makesit possible to make an optical pickup thin.

Another object of the present invention is to provide an objective-lensdriving device which makes it possible to make an optical pickup compactand thin and drive the objective lens stably in both the focusingdirection and the tracking direction.

Still another object of the present invention is to provide acartridge-type optical disk apparatus having a structure which makes itpossible to make the optical disk apparatus thin and compact.

A further object of the present invention is to provide anobjective-lens driving device which is easy to manufacture and iscapable of driving the objective lens with high accuracy.

In accordance with a first aspect of the present invention, there isprovided a mechanism for adjusting the inclination of an objective lensfor use in an optical pickup including an objective-lens driving device,having an objective lens, and an optical system block for transmittingand receiving light with respect to the objective lens, theobjective-lens driving device being mounted on a mounting base of theoptical system block. In the adjusting mechanism, a recessed portion ora through hole portion is formed in the mounting base of the opticalsystem block, a projecting portion of a bottom of the objective-lensdriving device is accommodated in the recessed portion or the throughhole portion, and an inclining fulcrum for inclining the objective lensand height adjusting means for inclining the objective-lens drivingdevice about the inclining fulcrum are provided in vicinities of therecessed portion or the through hole portion of the mounting base.

In accordance with a second aspect of the present invention, there isprovided a mechanism for adjusting the inclination of an objective lensfor use in an optical pickup including an objective-lens driving device,having an objective lens and a yoke, and an optical system block fortransmitting and receiving light with respect to the objective lens, theobjective-lens driving device being mounted on a mounting base of theoptical system block. In the adjusting mechanism, a movable plate with asubstantially U-shaped cross section which is formed integrally with theyoke is provided, a recessed portion or a through hole portion is formedin the mounting base of the optical system block, a lower portion of theyoke formed integrally with the movable plate is accommodated in therecessed portion or the through hole portion, and an inclining fulcrumfor inclining the objective lens and height adjusting means forinclining the objective-lens driving device about the inclining fulcrumare provided in vicinities of the recessed portion or the through holeportion of the mounting base.

In accordance with a third aspect of the present invention, in themechanism for adjusting the inclination of an objective lens accordingto the second aspect of the invention, the height adjusting meansincludes an urging member for upwardly urging the objective-lens drivingdevice from the mounting base of the optical system block, and a screwfor tightening the objective-lens driving device against the mountingbase of the optical system block.

In accordance with a fourth aspect of the present invention, there isprovided an optical disk apparatus in which a magnetic circuit of theobjective-lens driving device is disposed within a window area of alower shell of the optical disk. In a case where such a structure isadopted, to prevent the demagnetization of the optical disk, it ispreferred that optical disk-side opposite ends of a yoke constitutingthe magnetic circuit of the driving device for driving an objective lensbe magnetically short-circuited by a magnetic member.

In accordance with a fifth aspect of the present invention, there isprovided an optical disk apparatus in which opposite end portions, asviewed in a tracking direction, of an objective lens holder which areopposed to the disk are formed into inclined surfaces, so as to preventthe lens holder from colliding against an edge on the innermostperipheral side or outermost peripheral side of the window in the lowershell, and to prevent an increase in the vertical dimension of the lensholder. In addition, in the optical disk apparatus in which suchinclined surfaces are formed at the opposite end portions, as viewed inthe tracking direction, of the objective lens holder which are opposedto the disk, the magnetic circuit of the objective-lens driving deviceis preferably disposed within the window area of the lower shell of theoptical disk, and a portion of the objective lens holder which opposes aside edge of the window in the lower shell is preferably formed into aninclined surface.

In accordance with a sixth aspect of the present invention, there isprovided an objective-lens driving device comprising: a movable sectionincluding an objective lens, a focusing coil, and a tracking coil; and afixed section which includes a single magnetic circuit having a magneticgap and in which the focusing coil and the tracking coil are bothdisposed in the magnetic gap, wherein a point of application of aresultant force of a focusing-driving force generated by a magnetic fluxin the magnetic gap and a reversely-oriented focusing-driving forcegenerated outside the magnetic gap by a magnetic flux leaking from themagnetic gap is brought close to a point of application of atracking-driving force by controlling an amount of leakage magneticflux.

Furthermore, the weight of the movable section is distributed such thata position of a center of gravity of the movable section is locatedbetween the point of application of the tracking-driving force and thepoint of application of the resultant force of the focusing-drivingforces.

In accordance with a seventh aspect of the present invention, there isprovided an objective-lens driving device comprising: a movable sectionincluding an objective lens, a focusing coil, and a tracking coil; and afixed section which including a single magnetic circuit having amagnetic gap, both of the coils being disposed in the magnetic gap,wherein a point of application of a tracking-driving force, a point ofapplication of a resultant force of focusing-driving forces respectivelyoccurring in and outside the magnetic gap, and a position of a center ofgravity of the movable section are made to substantially coincide witheach other.

In accordance with an eighth aspect of the present invention, there isprovided an objective-lens driving device comprising: a movable sectionincluding an objective lens and a coil for generating a driving force ina predetermined direction; a resiliently supporting member serving as apath for supplying electric current to the coil and supporting themovable section in a cantilevered manner or on both sides thereof; aprinted circuit board electrically connected to at least one fixed endside of the resiliently supporting member; and a base having a yoke forgenerating the driving force; and an intermediate member for fixing theprinted circuit board and the base by molding in a state in which theprinted circuit board and the base are positioned relative to eachother.

In accordance with a ninth aspect of the present invention, in theobjective-lens driving device according to the eighth aspect of theinvention, the intermediate member has a guide hole for inserting theresiliently supporting member therethrough to connect the fixed end sideof the resiliently supporting member, and a damping-member accommodatingportion for accommodating a damping member for damping unwantedresonance of the movable section is formed in a vicinity of the guidehole.

In accordance with the mechanism for adjusting the inclination of anobjective lens according to the first aspect of the invention, thefulcrum for inclining the objective lens and the height adjusting meansare provided in the vicinities of the recessed portion or the throughhole portion formed in the mounting base of the optical system block,and it is thereby possible to make the optical pickup thin.

In accordance with the mechanism for adjusting the inclination of anobjective lens according to the second aspect of the invention, sincethe yoke and the movable plate are formed integrally, the optical pickupcan be made thin, and since the yoke and the movable plate are formedintegrally, the fabrication is facilitated.

In accordance with the mechanism for adjusting the inclination of anobjective lens according to the third aspect of the invention, theobjective-lens driving device can be inclined about the fulcrum forinclining the objective lens in accordance with the degree of tighteningof the screw, thereby inclining the objective lens.

In accordance with the objective-lens driving device according to thefourth aspect of the invention, since the magnetic circuit is disposedwithin the window in the lower shell, the dimension between the lowersurface of the magnetic circuit of the driving device and the lowersurface of the lower shell can be reduced, thereby making it possible toobtain a thin device. In addition, according to the fifth aspect of theinvention, since the radially opposite end portions of the objectivelens holder, which are opposed to the disk, are formed into inclinedsurfaces, it is possible to make the lens holder thin.

In accordance with the objective-lens driving device according to thesixth aspect of the invention, since the point of application of theresultant force of focusing-driving forces respectively occurring in andoutside the magnetic gap is brought close to the point of application ofthe tracking-driving force, their distances with respect to the positionof the center of gravity of the movable section can both be reduced.Therefore, it is possible to easily prevent the occurrence of unwantedresonance in both the focusing direction and the tracking direction.Furthermore, since the position of the center of gravity of the movablesection can be located between the point of application of thetracking-driving force and the point of application of the resultantforce of the focusing-driving forces respectively occurring in andoutside the magnetic gap, the distances between the position of thecenter of gravity of the movable section and the point of application ofthe resultant force and between the position of the center of gravity ofthe movable section and the point of application of the tracking-drivingforce are both made short. Therefore, it is possible to prevent theoccurrence of unwanted resonance in both the focusing direction and thetracking direction.

In accordance with the objective-lens driving device according to theseventh aspect of the invention, the focusing coil and the trackingcoils are disposed in the magnetic gap, so that the objective-lensdriving device can be made compact and thin. In addition, since thepoint of application of the tracking-driving force and the position ofthe center of gravity of the movable section are made to substantiallycoincide with each other, it is possible to make the device compact andthin. Hence, it is possible to realize a stable servomechanism in whichunwanted resonance does not occur in both the focusing direction and thetracking direction.

In accordance with the objective-lens driving device according to theeighth aspect of the invention, since the printed circuit board and thebase are secured to each other by being positioned relative to eachother when the intermediate member is formed by molding, a bondingprocess and a screw-tightening process can be omitted in assembling theprinted circuit board, the base, and the intermediate member. Hence, therelative positional accuracy between the printed circuit board and thebase can be improved.

In accordance with the objective-lens driving device according to theninth aspect of the invention, since the damping member is accommodatedin the damping-member accommodating portion, the damping membersuppresses the vibration of the resiliently supporting member, therebydamping the unwanted resonance of the movable section.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an objective-lens driving device fordescribing a conventional mechanism for adjusting the inclination of anobjective lens;

FIG. 2 is a cross-sectional view of the conventional mechanism foradjusting the inclination of an objective lens;

FIG. 3 is a perspective view of another conventional mechanism foradjusting the inclination of an objective lens;

FIG. 4 is a perspective view of still another conventional mechanism foradjusting the inclination of an objective lens;

FIG. 5A is a schematic diagram illustrating an optical disk apparatus ofa cartridge type;

FIG. 5B is an exploded perspective view illustrating a schematicarrangement of an optical disk and a cartridge;

FIGS. 6A and 6B are diagrams of dimensional relationships among variousparts in a conventional example and in this embodiment, respectively, inwhich the optical disk apparatuses are viewed in a tracking direction;

FIG. 7 is a is a perspective view of a conventional objective-lensdriving device;

FIG. 8 is a side view illustrating a mechanism for preventing unwantedresonance;

FIG. 9 is a cross-sectional view illustrating a conventional problem;

FIG. 10 is a cross-sectional view illustrating another conventionalproblem;

FIG. 11 is a cross-sectional view of an optical pickup in accordancewith a first embodiment of the present invention, and illustrates oneexample of a mechanism for adjusting the inclination of an objectivelens;

FIG. 12 is an exploded perspective view of the mechanism for adjustingthe inclination of an objective lens;

FIG. 13 is a perspective view illustrating another example of a movableplate shown in FIG. 12;

FIG. 14 is a vertical cross-sectional view illustrating an optical diskapparatus in accordance with a second embodiment of the presentinvention;

FIG. 15 is a perspective view of the optical disk apparatus shown inFIG. 14;

FIG. 16 is a perspective view illustrating a magnetic circuit of anobjective-lens driving device in accordance with the second embodiment;

FIGS. 17A and 17B are diagrams of dimensional relationships amongvarious parts on the outer peripheral side or inner peripheral side ofthe disk in a conventional example and a comparative example,respectively;

FIG. 18 is a diagram of dimensional relationships among various parts inaccordance with the second embodiment;

FIG. 19 is a perspective view of an essential portion of anobjective-lens driving device in accordance with a third embodiment ofthe present invention;

FIG. 20 is a vertical cross-sectional view of FIG. 20;

FIG. 21 is a horizontal cross-sectional view of FIG. 20;

FIG. 22 is a diagram illustrating the relationships between variousdriving forces and the position of the center of gravity;

FIG. 23 is a graph illustrating the relationship between the thicknessof an upper yoke on the one hand, and a in-gap magnetic flux density anda leakage magnetic flux density, on the other;

FIG. 24 is a graph illustrating the effect of the thickness of aU-shaped yoke with respect to pitching resonance in accordance with thethird embodiment;

FIG. 25 is a diagram illustrating the positional relationships amongrespective points of application;

FIG. 26 is a diagram of a transmission characteristic in accordance withthe third embodiment;

FIG. 27 is a diagram of a transmission characteristic in anotherexample;

FIG. 28 is a diagram of a transmission characteristic in still anotherexample;

FIG. 29 is a side view of an objective-lens driving device in accordancewith a fourth embodiment of the present invention;

FIG. 30 is a perspective view of a yoke in accordance with the fourthembodiment;

FIG. 31 is a side view illustrating a method of fabrication inaccordance with the fourth embodiment;

FIG. 32 is another side view illustrating the method of fabrication inaccordance with the fourth embodiment;

FIG. 33 is a plan view illustrating the method of fabrication inaccordance with the fourth embodiment; and

FIG. 34 is a cross-sectional view taken along the line C—C in FIG. 33.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, a description will be givenof the preferred embodiments of the present invention.

First Embodiment

FIG. 11 is a cross-sectional view of an optical pickup in accordancewith a first embodiment of the present invention, and illustrates oneexample of a mechanism for adjusting the inclination of an objectivelens. FIG. 12 is an exploded perspective view thereof.

First, a description will be given of an optical pickup to which amechanism 130 for adjusting the inclination of an objective lens inaccordance with this embodiment is applied.

As shown in FIG. 11, this optical pickup is comprised of anobjective-lens driving device 110 having an objective lens 111 and anoptical system block 120 for transmitting and receiving light to andfrom the objective lens 111, in addition to the mechanism 130 foradjusting the inclination of an objective lens. The objective-lensdriving device 110 is disposed on a mounting base 121 of the opticalsystem block 120.

The objective-lens driving device 110 has a lens holder 112 for holdingthe objective lens 111, an unillustrated driving coil for driving thelens holder 112 in the focusing direction and the tracking direction, ayoke 114 which constitutes a magnetic circuit together with a permanentmagnet 113, and projects from the bottom side of the objective-lensdriving device 110, and a supporting base 116 which also serves as apath for supplying electric current to the driving coil and supports thelens holder 112 side via a bundling member 115.

The optical system block 120 is provided with the mounting base 121 onwhich the objective-lens driving device 110 is disposed, and is furtherprovided with an optical system which includes a light-beam generatingsource, such as a semiconductor laser, and optical elements, such as abeam splitter, as well as a light detecting element for receiving areflected light beam. In this optical system block 120, a light beam ismade incident upon the objective lens 111 from the light-beam generatingsource via the optical system, and a light spot is formed on the opticaldisk by the objective lens 111. The light beam reflected from theoptical disk is received by the light detecting element via the opticalsystem, and a light detection signal corresponding to the intensity ofthe reflected light beam thus received is outputted.

Next, a description will be given of the mechanism 130 for adjusting theinclination of an objective lens in accordance with this embodiment,which is used in the above-described optical pickup.

This mechanism 130 for adjusting the inclination of an objective lenshas a movable plate 131 for fixedly disposing the objective-lens drivingdevice 110, and a through hole portion 132 is formed in the mountingbase 121 of the optical system block 120. A lower portion of the yoke114 projecting from the bottom side of the objective-lens driving device110 is accommodated in the through hole portion 132, and an incliningfulcrum 133 for inclining the objective lens 111 and a height adjustingmeans 134 for inclining the objective-lens driving device 110 about theinclining fulcrum 133 are provided in the vicinities of the through holeportion 132 of the mounting base 121.

The height adjusting means 134 is provided with an urging member 135,such as a leaf spring, for upwardly urging the objective-lens drivingdevice 110 from the mounting base 121 side of the optical system block120, as well as two height adjusting screws 136 for tightening theobjective-lens driving device 110 toward the mounting base 121 side ofthe optical system block 120.

The movable plate 131 has a substantially U-shaped cross section forconnecting collars 131 a on both sides thereof and a bottom 131 b. Thesupporting base 116 of the objective-lens driving device 110 is fixedlydisposed on this movable plate 131. In addition, a notch 131 c is formedin the bottom 131 b of the movable plate 131 so that the yoke 114 of theobjective-lens driving device 110 can enter the lower side. As a result,the thickness of the movable plate 131 and the thickness of theinclination adjusting mechanism 130 are not affected by the thickness ofthe optical pickup, thereby making it possible to reduce thethicknesswise dimension. In addition, one collar 131 a of the movableplate 131 has a spherical-portion receiving hole 131 d, and the othercollar 131 a has two female screws 131 e for threadedly engaging withthe height adjusting screws 136, respectively.

The spherical-portion receiving hole 131 d, which is formed in themovable plate 131 and has a smaller diameter than a spherically convexportion 137, is received on the spherically convex portion 137 formed onthe mounting base 121 of the optical system block 120. A lower edge ofthe spherical-member receiving hole 131 d is made to abut against thesurface of the spherically convex portion 137, thereby forming theinclining fulcrum 133.

Next, a description will be given of a method of adjusting theinclination in accordance with this embodiment.

First, after the objective-lens driving device 110 is assembled, theobjective-lens driving device 110 is fixedly disposed on the movableplate 131. The yoke 114 of the objective-lens driving device 110 entersthe lower side through the notch 131 c formed in the movable plate 131without interfering with the movable plate 131. The movable plate 131 isplaced on the mounting base 121 of the optical system block 120. Thebottom 131 b of the movable plate 131 enters the lower side withoutinterfering with the mounting plate 121 through the opening 132 formedin the mounting plate 121 of the optical system block 120. The loweredge of the spherical-member receiving hole 131 d and the surface of thespherically convex portion 137 abut against each other, with the resultthat the fulcrum 133 for inclining the objective lens 111 is formed.Then, the height adjusting screws 136 are inserted through insertionholes 121 d provided in the mounting base 121, and are made tothreadedly engage with the female screws 131 e of the movable plate 131.The movable plate 131 is set in a state in which it is pushed upwardlyabout the inclining fulcrum 133 by the urging member 135.

Here, as the degree of tightening of one or both of the two heightadjusting screws 136 is adjusted, as required, the objective-lensdriving device 110 is inclined about the inclining fulcrum 133 inaccordance with the degree of tightening. Thus, it is possible to adjustthe inclination of the objective lens 111 in the direction of the X-axis(jitter direction) and the direction of the Y-axis (tracking direction).

In accordance with this embodiment arranged as described above, sincethe inclining fulcrum 133 and the height adjusting means 134 areprovided in the vicinities of the through hole portion 132 formed in themounting base 121 of the optical system block 120, it is possible tomake the optical pickup thin. Also, since the objective-lens drivingdevice 110 is inclined about the inclining fulcrum 133 in accordancewith the degree of tightening of the height adjusting screws 136, theadjustment of the inclination of the objective lens 111 can be effectedeasily. In addition, since the lower portion of the yoke 114 projectingfrom the bottom of the objective-lens driving device 110 is accommodatedin the opening 132 formed in the mounting base 121 of the optical systemblock 120, the optical pickup can be made thin substantially by theportion of the thickness of the mounting base 121 of the optical systemblock 120. Further, since the arrangement provided is such that theinclination can be adjusted by one inclining fulcrum 133 and the twoadjusting points, and the urging member 135 is disposed outside one side138 a, opposing the inclining fulcrum 133, of a triangle 138 formed bythe three points, it is possible to appropriately pressurize thespherically convex portion 137 and realize the inclination of theoptical axis in the X-axis direction and the Y-axis direction smoothlyin a saved space. Moreover, since the spherically convex portion 137projects from the mounting base 121 of the optical system block 120, thespherically convex portion 137 can be formed integrally through diecasting or injection molding, and the inclination of the optical axis inthe X-axis direction and the Y-axis direction can be realized with asmall number of component parts.

It should be noted that the present invention is not confined to theabove-described embodiment, and various modifications are possible. Forexample, an arrangement may be provided such that, as shown in FIG. 13,the yoke (114) is formed by uprightly raising portions 131 f of thebottom 131 b of a movable plate 131′, and the movable plate and the yokeare formed integrally by a metal-pressed component. In this case, theheightwise positions of the bottoms of the yoke (114) and the movableplate 131′ can be set at the same level, so that the optical pickup canbe made thinner and fabrication is facilitated. In addition, anarrangement may be alternatively provided such that a concave portion isformed in the mounting base 121, while a spherically convex portion isformed on the movable plate 131 or 131′ so as to form the fulcrum forinclining the objective lens 111.

In accordance with the first embodiment detailed above, since thefulcrum for inclining the objective lens and the height adjusting meansare provided in the vicinities of the recessed portion or the throughhole portion formed in the mounting base of the optical system block, itis possible to make the optical pickup thin.

In addition, since the yoke and the movable plate are formed integrally,the optical pickup can be made thin, and the fabrication is facilitated.

Further, since the urging member and the screws are used, theobjective-lens driving device can be inclined about the fulcrum forinclining the objective lens, so that the adjustment of the inclinationof the objective lens can be effected easily.

Furthermore, since two or more adjustment screws are provided,adjustment in the jitter direction and the tracking direction becomespossible.

Also, the spherically convex portion constituting the inclining fulcrumis formed integrally with the mounting base, the fabrication of themounting base is facilitated.

Second Embodiment

Next, a description will be given of a second embodiment.

FIG. 14 is a vertical cross-sectional view illustrating an optical diskapparatus in accordance with a second embodiment of the presentinvention. FIG. 15 is a perspective view thereof. In FIGS. 14 and 15,reference numeral 311 denotes a base formed of a resin or the like, anda U-shaped yoke 310 constituting a magnetic circuit for driving theobjective lens 303 as well as a reflecting mirror 320 are fixed on thebase 311. Permanent magnets 312 are fixed on opposing surfaces of theyoke 310, respectively, and are magnetized in the left-and-rightdirection, as shown in FIG. 14. A support 315 formed of a resin is fixedat one end of the base 311 by means of screws 316, and the support 315and a lens holder 313 are connected to each other by means of four wiresprings 314. These wire springs 314 have their root portions penetratingthe support 315. Proximal ends of the springs 314 are secured bysoldering 317 to a printed circuit board 315 a which is fixed to thesupport 315 by bonding or the like, while distal ends of the springs 314are fixed by soldering 317 to a pair of printed circuit boards 313 ewhich are respectively fixed to both sides of the lens holder 313 bybonding or the like. The lens holder 313 is arranged such that theobjective lens 303 is attached to one end thereof and a remainingportion is formed as a frame 313 a. The yoke 310 to which the permanentmagnets are fixed is inserted in the frame 313 a in such a manner as tobe relatively movable. That is, as shown in the perspective view of FIG.16, a focusing coil 318 is formed in a rectangular shape, a pair oftracking coils 319 is fixed on one surface thereof, and the focusingcoil 318 is inserted and fixed in the frame 313 a such that the focusingcoil 318 surrounds one of the permanent magnets 312 and one columnportion 310 a to which it is fixed, with a predetermined distance. Asshown in FIG. 16, the portion of the focusing coil 318 to which thetracking coils 319 are fixed is inserted between the pair of permanentmagnets 312.

With respect to a magnetic circuit 309 of the device for driving theobjective lens 303, if the current is allowed to flow across thefocusing coil 318 in the direction of arrow i1, as shown in FIG. 16, amagnetic flux φ generated between the pair of permanent magnets 312crosses the coil through which this current flows. As a result, thefocusing coil 318, i.e., the lens holder 313, is urged in a direction inwhich it approaches an optical disk 301, as indicated by the arrow F₃₁,and the lens holder 313 becomes stationary where it balances with theresiliency of the wire springs 314. If the direction of the current isreversed, the lens holder 313 is urged in a direction in which it movesaway from the optical disk 301. Meanwhile, if a current i2 is allowed toflow across vertically oriented portions a of the pair of tracking coils319, the lens holder 313 is subjected to a force acting in the directionof the arrow F₃₂ (the tracking direction=the radial direction of theoptical disk), and if the direction of the current is reversed, thedirection of the acting force is also reversed. It should be noted thatthe tracking coils 319 are arranged in an area outside the area betweenthe opposing portions of the pair of permanent magnets 312 so that theamount of the magnetic flux crossing at portions b on both sides of thetracking coils 319 is reduced.

In the present invention, the magnetic circuit 309 of the device fordriving the objective lens 303, together with the objective lens 303, isdisposed within a window 308 d of a lower shell 308 b, as shown in FIG.14. Since the magnetic circuit 309 is disposed within the area of thewindow 308 d, as shown in FIG. 6B, it is possible to reduce thedimension L₃₁₀ from the lower surface of the lower shell 308 b to thelower surface of the magnetic circuit 309, thereby making it possible tomake the apparatus thin and compact. In this case, distal ends of theyoke 310 are magnetically short-circuited by a short-circuiting member321 having high permeability, such as iron, so that the magneticallyrecorded surface of the optical disk 301 will not be demagnetized by themagnetic field generated by the permanent magnets 312.

In addition, as shown in FIG. 15, opposite end portions 313 b, as viewedin the tracking direction, of the lens holder 313 are formed intoinclined surfaces, thereby making it possible to reduce the thickness ofthe lens holder 313. A description will be given of this point withreference to FIGS. 17A, 17B, and 18. As shown in FIG. 17A, the lensholder 313 requires the width L₃₅ of the magnetic circuit 309 (yoke 310)so as to drive the lens holder 313 in the focusing direction and thetracking direction. In addition, the lens holder requires mechanicalleeway for moving in the tracking direction, i.e., an arbitrarydimension is required as the gap (L₃₆−L₃₅) between the width inside theframe 313 a and the yoke 310. Furthermore, it is necessary to secure thewidth of the frame 313 a of the lens holder 313. Consequently, a widthL₃₇ which is substantially larger than the diameter of the objectivelens 303 is required as a whole. In the lens holder 313 which requiressuch a width L₃₇, if the opposite end portions of the lens holder 313 asviewed in the radial direction of the optical disk are formed intosquare shapes in the conventional manner, in a case where the objectivelens 303 is driven in the focusing direction in a state in which theobjective lens 303 has been moved to the innermost peripheral side oroutermost peripheral side of the optical disk 301, the lens holder 313does not enter inside the window 308 d, and collides against the lowersurface of the lower shell 308 b. This occurs due to the fact that thedistance L₃₄ between the upper portion of the lens holder 313 and thelower shell 308 b is smaller than the amount of movement in the upwarddirection for focusing, as shown in FIG. 17A. However, if this distanceis made greater as indicated by L₃₈ in FIG. 17B, the distance L₃₉between the lower surface of the lower shell 308 b to the lower surfaceof the magnetic circuit 309 would become greater (if the workingdistance of the objective lens 303 is fixed).

In contrast, in this embodiment, as shown in FIG. 18, since the sidesurfaces 313 b of the lens holder 313 are inclined, it is possible toreduce the thickness of the lens holder 313 without undermining thestrength of the lens holder 313 while the vertical distance between thelens holder 313 and an edge d on the innermost peripheral side oroutermost peripheral side of the window 308 d is kept at the largedistance L₃₈ in the same way as in FIG. 17B. As a result, it is possibleto reduce the overall thickness L₃₁₀ from the lower surface of the lowershell 308 b to the lower surface of the magnetic circuit 309.

As shown in FIGS. 14 and 6B, if a portion 313 c of the lens holder 313which opposes a side edge e of the window 308 d in the lower shell 308 bis formed into an inclined surface for a similar reason, it is possibleto make the apparatus thin and compact for the same reason.

It should be noted that the arrangement of the magnetic circuit 309, thestructure for supporting the lens holder 313, and the like in theabove-described embodiment are only illustrative, and it goes withoutsaying that various modifications are possible.

In accordance with the above-described second embodiment, in thecartridge-type optical disk apparatus, since the magnetic circuit of theobjective-lens driving device is disposed inside the window area of thelower shell, it is possible to make the optical pickup thin and compact.

In addition, since the optical disk-side opposite ends of the yoke ofthe magnetic circuit of the objective-lens driving device aremagnetically short-circuited by a magnetic member, the magneticallyrecorded surface of the optical disk is prevented from beingdemagnetized despite the fact that the magnetic circuit is brought intoclose proximity to the optical disk.

In addition, since the opposite end portions, as viewed in the trackingdirection, of the objective lens holder which are opposed to the diskare formed into inclined surfaces, it is possible to make the apparatusthin and compact while securing the strength of the lens holder andmechanical leeway during movement in the focusing direction and thetracking direction.

Moreover, since the magnetic circuit of the objective-lens drivingdevice is disposed within the window area of the lower shell of theoptical disk, and a portion of the objective lens holder which opposes aside edge of the window in the lower shell is formed into an inclinedsurface, the apparatus can be made further thin and compact.

Third Embodiment

Hereafter, a description will be given of a third embodiment of thepresent invention with reference to the drawings.

FIG. 19 is a perspective view of an essential portion illustrating anexample of the objective-lens driving device in accordance with thethird embodiment of the present invention. FIG. 20 is a verticalcross-sectional view thereof, and FIG. 21 is a horizontalcross-sectional view thereof.

An objective-lens driving device 210 in the third embodiment iscomprised of a movable section 213 including an unillustrated objectivelens, an unillustrated lens holder for holding the objective lens, afocusing coil 211 secured to the lens holder, a pair of tracking coils212, and the like; and a fixed section 217 which has a magnetic circuitconstituted by a U-shaped yoke 214, an upper yoke 215, and a pair ofmagnets 216 a and 216 b, and supports the movable section 213 by meansof unillustrated spring members serving as paths for supplying currentto the respective coils 211 and 212 of the movable section 213.

The U-shaped yoke 214 of the fixed section 217 is formed with a U-shapedcross section such that a pair of a first leg 214 a and a second leg 214b are opposed to each other. The upper yoke 215 is secured to distal endfaces of the first and second legs 214 a and 214 b of the U-shaped yoke214. The pair of magnets 216 a and 216 b are disposed on therespectively inner sides of the first and second legs 214 a and 214 b ofthe U-shaped yoke 214 so that different poles, i.e., the S pole and theN pole, are opposed to each other. A magnetic gap 218 is formed betweenthe pair of magnets 216 a and 216 b.

The focusing coil 211 of the movable section 213 is formed by winding acoil member around its central axis such that its cross section becomesa hollow rectangle. The focus coil 211 is disposed around the first leg214 a of the U-shaped yoke 214 with a gap therebetween such that itscentral axis becomes parallel to an optical axis 219, and a portion ofthe focus coil 211 passes the magnetic gap 218. Consequently, if currentis supplied to the focusing coil 211, the unillustrated lens holdermoves in the focusing direction (in the direction of the optical axis)Z. In addition, each of the tracking coils 212 is wound in such a manneras to allow the current to flow in the focusing direction Z, and issecured on the magnetic gap 218 side of the focusing coil 211. As aresult, if current is supplied to the tracking coils 212, theunillustrated lens holder moves in the perpendicular direction Y withrespect to the optical axis 219.

In the objective-lens driving device 210 of this embodiment, variousparts are so designed that, as shown in FIG. 22, a point of application212 t of a tracking-driving force generated by the tracking coils 212, apoint of application 212 f of a resultant force (F₂₁+F₂₂) of an in-gapfocusing-driving force F₂₁ occurring within the magnetic gap 218 and anoutside-gap focusing-driving force F₂₂ occurring outside the magneticgap 218 (on the outer side of the first leg 214 a), and the position 213a of the center of gravity of the overall movable section 213 includingthe objective lens and the lens holder, substantially coincide with eachother at a given point in a direction X tangential to the track (in adirection perpendicular to the focusing direction Z and the trackingdirection Y).

Specifically, various parts are designed in accordance with thefollowing technique. Namely, if it is assumed that the distance in thedirection X tangential to the track between the position of the centerof gravity 213 a of the movable section 213 and a point of application211 a of the focusing-driving force F₂₁ occurring within the magneticgap is L₀, that the distance between the point of application 212 t ofthe tracking-driving force and the point of application 211 a of thefocusing-driving force F₂₁ occurring within the magnetic gap 218 is L₂₁,that the distance between the point of application 211 a of thefocusing-driving force F₂₁ occurring within the magnetic gap 218 and theresultant force (F₂₁+F₂₂) of the in-gap focusing-driving force F₂₁ andthe outside-gap focusing-driving force F₂₂ is L₂₂, that the distancebetween the point of application 211 a of the in-gap focusing-drivingforce F₂₁ and a point of application 211 b of the outside-gapfocusing-driving force F₂₂ is L₂₃, that the in-gap magnetic flux densityoccurring within the magnetic gap 218 is B₁, and that the outside-gapmagnetic flux density (hereafter referred to leakage magnetic fluxdensity) occurring in a portion where the outside-gap focusing-drivingforce F₂₂ acts is B₂, the following relationships hold:

L ₂₂ =F ₂₂ ·L ₂₃/(F ₂₁ −F ₂₂)=B ₂ ·L ₂₃/(B ₁ −B ₂)  (1)

The reason for this is that if the effective width L and the current Iare assumed to be fixed, the driving force F is in a proportionalrelationship with the magnetic flux density B.

Accordingly, the values of L₀, L₂₁, L₂₂, L₂₃, B₁, and B₂ are selected insuch a way that L₂₂ on the one hand, and L₂₁ and L₀ on the other, becomesubstantially equal.

Consequently, since the point of application 212 f of the resultantforce (F₂₁+F₂₂), the point of application 212 t of the tracking-drivingforce generated by the tracking coils 212, and the position 213 a of thecenter of gravity of the overall movable section 213 substantiallycoincide with each other at a given point in the X direction, it ispossible to prevent the occurrence of unwanted resonance.

Referring also to FIGS. 23 and 24, a description will be given of theeffects of the embodiment arranged as described above.

FIG. 23 is a graph illustrating the relationship between the thicknessof the upper yoke 215 on the one hand, and the in-gap magnetic fluxdensity B₁, and the leakage magnetic flux density (outside-gap magneticflux density) B₂, on the other. FIG. 24 is a graph illustrating theeffect of the thickness of the U-shaped yoke 214 with respect to thepitching resonance, and is a graph which illustrates the phase and themagnitude (gain) of resonance (pitching resonance) in a mode of rotationabout the Y-axis.

According to this embodiment, since the focusing coil 211 and thetracking coils 212 are disposed within one magnetic gap 218, it ispossible to make the device compact and thin.

Also, as is apparent from FIG. 23, the in-gap magnetic flux density B₁,and the leakage movable plate B₂ change with the thickness of the upperyoke 215, and the greater the thickness of the upper yoke 215, thegreater the in-gap magnetic flux density B₁, becomes and the smaller theleakage magnetic flux density B₂ becomes. Accordingly, at an arbitrarydistance L₂₃, the greater the thickness of the upper yoke 215, thesmaller L₂₂ becomes, and the point of application 212 f of the resultantforce (F₂₁+F₂₂) approaches the point of application 211 a of the in-gapfocusing-driving force F₂₁. Therefore, in a case where L₂₁ and L₂₃ arefixed as dimensions, if the thickness of the upper yoke 215 is set to anappropriate value so that the values of B₁, and B₂ become such thatL₂₁=L₂₂, the point of application 212 t of the tracking-driving force,the point of application 212 f of the resultant force (F₂₁+F₂) of thein-gap focusing-driving force F₂₁, and the outside-gap focusing-drivingforce F₂₂, and the position 213 a of the center of gravity of theoverall movable section 213 substantially coincide with each other at agiven point in the X direction. Since the point of application 212 t ofthe tracking-driving force and the position 213 a of the center ofgravity of the overall movable section 213 substantially coincide witheach other, it is possible to prevent the occurrence of resonance aboutthe Z-axis with the position 213 a of the center of gravity set as thecenter. Since the point of application 212 f of the resultant force(F₂₁+F₂₂) and the position 213 a of the center of gravity of the movablesection 213 substantially coincide with each other, it is possible toprevent the occurrence of resonance about the Y-axis with the position213 a of the center of gravity set as the center. Thus, by making activeuse of the outside-gap focusing-driving force F₂₂, which hasconventionally been considered as being needed to be minimized, itbecomes possible to prevent the occurrence of unwanted resonance in boththe tracking direction Y and the focusing direction Z.

In addition, as is apparent from FIG. 24, if the thickness of the upperyoke 215 is set to an appropriate value, it is possible to prevent theoccurrence of pitching resonance.

Also, although a measure against the focusing side is adopted in theobjective-lens driving device disclosed in Unexamined Japanese PatentApplication (Kokai) 4-102235 in the known example, this embodiment hasan advantage in that it is capable of coping with the tracking side aswell.

FIG. 25 is a diagram illustrating the positional relationships among therespective points of application 211 a, 212 f, and 212 t and theposition 213 a of the center of gravity in the direction X tangential tothe track in accordance with a modification of the objective-lensdriving device of the present invention. This modification differs fromthe above-described embodiment in the relationships among the respectivepoints of application 211 a, 212 f, and 212 t and the position 213 a ofthe center of gravity, and the other aspects are similar to those of theabove-described embodiment.

In this embodiment, various parts are arranged such that|L₂₁−L₂₂|<|L₂₁|, and L₀ is determined such that L₂₁≧L₀≧L₂₂ (whenL₂₁≧L₂₂) or L₂₁≦L₀≦L₂₂ (when L₂₁≦L₂₂).

Referring to FIGS. 26 to 28 as well, a description will be given of theeffects of this modification.

FIG. 26 is a diagram of a transmission characteristic of an actuator inthe focusing direction Z when settings were provided such that L₀=200μm, L₂₁=400 μm, and L₂₂=150 μm, and S₂=50 μm, and S₁=200 μm. FIG. 27 isa diagram of a transmission characteristic of the actuator when theposition 213 a of the center of gravity and the position of the point ofapplication 212 f were arranged reversely, and the value of S₂ wassimilarly set to 50 μm. FIG. 28 is a diagram of a transmissioncharacteristic of the actuator in the tracking direction Y when settingswere provided such that L₀=200 μm, L₂₁=400 μm, and L₂₂=250 μm, and S₂=50μm, and S₁=200 μm. Additionally, portions indicated by dotted-dash-linecircles in FIGS. 26 to 28 show points of resonance.

As is apparent from FIG. 26, resonance of the frequency of rotationabout the Y-axis with the position 213 a of the center of gravity set asthe center appeared in the portion indicated by the dotted-dash-linecircle, but the resonance was sufficiently small. Accordingly , as shownin FIG. 25, if the distance S between the point of application 212 t ofthe tracking-driving force and the point of application 212 f of theresultant force (F₂₁+F₂₂), i.e., an actual focusing-driving force, ismade short, and the position 213 a of the center of gravity of theoverall movable section 213 is disposed within that distance (S), it ispossible to reduce both the distance S₁ between the position 213 a ofthe center of gravity and the point of application 212 t and thedistance S₂ between the position 213 a of the center of gravity and thepoint of application 212 f as compared with conventional examples,thereby making it possible to sufficiently reduce the occurrence ofunwanted resonance in the two directions.

As is apparent from FIG. 27, resonance of the frequency of rotationabout the Y-axis with the position 213 a of the center of gravity set asthe center appeared in the portion indicated by the dotted-dash-linecircle. If a comparison is made with FIG. 26, although the phase wasreversed, the value of resonance was sufficiently small. As is apparentfrom FIG. 28, resonance of the frequency of rotation about the Z-axiswith the position 213 a of the center of gravity set as the centerappeared in the portion indicated by the dotted-dash-line circle, butthe resonance was sufficiently small. Accordingly, even if the position213 a of the center of gravity of the overall section 213 is notdisposed between the point of application 212 t of the tracking-drivingforce and the point of application 212 f of the actual focusing-drivingforce (resultant force), insofar as S₁ and S₂ are sufficiently small, itis possible to reduce the occurrence of unwanted resonance to asufficiently small level. Thus, if S₁ and S₂ are made small, theunwanted resonance can be made sufficiently small by making S small,without adopting the above-described arrangement.

It should be noted that the present invention is not limited to theabove-described embodiment, and may be implemented by adopting variousmodifications. For example, in order to control the values of the in-gapmagnetic flux density B₁, and the leakage magnetic flux density B₂, thethickness, the shape and the like of one leg 214 a of the yoke 214 maybe devised, and various values including L₂₁ and L₂₃ may be determinedsuch that L₂₁=L₂₂.

In accordance with the third embodiment of the present inventiondetailed above, the following advantages are obtained.

Since the point of application of the resultant force offocusing-driving forces respectively occurring in and outside themagnetic gap is brought close to the point of application of thetracking-driving force, their distances with respect to the position ofthe center of gravity of the overall movable section can both bereduced. Therefore, it is possible to easily prevent the occurrence ofunwanted resonance in both the focusing direction and the trackingdirection.

Further, since the position of the center of gravity of the overallmovable section is located between the point of application of thetracking-driving force and the point of application of the resultantforce of the focusing-driving forces respectively occurring in andoutside the magnetic gap, the distances between the position of thecenter of gravity of the overall movable section and the point ofapplication of the resultant force and between the position of thecenter of gravity of the overall movable section and the point ofapplication of the tracking-driving force are both made short.Therefore, it is possible to prevent the occurrence of unwantedresonance in both the focusing direction and the tracking direction.

Additionally, since various parts are arranged in such a manner as tosatisfy the formulae: |L₀−L₂₂|≦50 μm and |L₀−L₂₁|≦200 μm, it is possibleto reduce unwanted resonance.

Furthermore, since the arrangement provided is such that the focusingcoil and the tracking coils are disposed in a single magnetic circuit,and the point of application of the tracking-driving force, the point ofapplication of the resultant force of focusing-driving forcesrespectively occurring in and outside the magnetic gap, and the positionof the center of gravity of the movable section are made tosubstantially coincide with each other, it is possible to make thedevice compact and thin. Hence, it is possible to realize a stableservomechanism in which unwanted resonance does not occur in both thefocusing direction and the tracking direction.

Moreover, since the arrangement provided is such that the focusing coiland the tracking coils are disposed in a single magnetic circuit, thepoint of application of the tracking-driving force, the point ofapplication of the resultant force of focusing-driving forcesrespectively occurring in and outside the magnetic gap, and the positionof the center of gravity of the movable section are made tosubstantially coincide with each other by selecting the values of L₀,L₂₁, L₂₂, L₂₃, B₁, and B₂ in such a manner as to satisfy theaforementioned formula, it is possible to make the device compact andthin. Hence, it is possible to realize a stable servomechanism in whichunwanted resonance does not occur in both the focusing direction and thetracking direction. In addition, since the values of L₀, L₂₁, L₂₂, L₂₃,B₁, and B₂ can be selected as required, design of a high degree offreedom is possible. Also, since the present invention can be arrangedon the basis of magnetic flux density which is easier to measure thanthe driving force, the design of various parts is facilitated.

Furthermore, as shown in FIG. 4, in the case that the objective-lensdriving device is made thin by arranging the magnetic circuit of thedriving device within the window area of the lower shell of the opticaldisk, the magnetic circuit is required to be minimized. If the symmetryof the magnetic circuit is unbalanced, undesired resonance may occur.According to the invention, this undesired resonance is prevented.

Fourth Embodiment

Hereafter, a description will be given of a fourth embodiment of thepresent invention with reference to the drawings.

FIG. 29 is a side view illustrating another example of theobjective-lens driving device in accordance with the fourth embodimentof the present invention.

As shown in the drawing, an objective-lens driving device 410 in thisembodiment is comprised of a movable section 412 including an objectivelens 411 and unillustrated coils for generating driving forces inpredetermined directions Y and Z; a plurality of (in this embodiment,four) wires 414 serving as resiliently supporting members for supportingthe movable section 412 in a cantilevered manner and also serving aspaths for supplying electric current to the coils; a printed circuitboard 413 electrically connected to fixed ends of the wires 414; a yokebase 415 for producing the driving forces; and an intermediate member416 for fixing the printed circuit board 413 and the yoke base 415 bymolding in a state in which the printed circuit board 413 and the yokebase 415 are positioned relative to each other.

The movable section 412 has an unillustrated lens holder to which anobjective lens 402 is secured, and a focusing coil and tracking coils(not shown) for driving the objective lens 402 in the focusing directionZ and the tracking direction Y are arranged in the lens holder.

As shown in the perspective view in FIG. 30, the yoke base 415 is formedas a substantially U-shaped yoke portion 415 a and a substantiallyZ-shaped placing portion 415 b for placing the printed circuit board 413thereon are formed integrally by press-working a metal plate. Theplacing portion 415 b is provided with through holes 415 c forstrengthening a joining force with respect to the intermediate member416.

As shown in FIG. 29, the printed circuit board 413 has four throughholes 413 a, which also serve as through holes for the wires 414, so asto strengthen the joining force between the printed circuit board 413and the intermediate member 416. On an outer surface 413 b of theprinted circuit board 413, soldered land portions which are providedwith plating are respectively formed around the through holes 413 a forconnecting external connecting cables.

The intermediate member 416 is formed of an injection molding membersuch as a plastic resin. When this intermediate member 416 is formed byinjection molding, the printed circuit board 413 and the yoke base 415are secured to each other. In addition, when the intermediate member 416is formed, guide holes 416 a for the insertion of the wires 414, as wellas a damping-member accommodating portion 416 b for filling a dampingmember 418 such as silicone in the vicinities of the guide holes 416 a,are also formed.

Next, also referring to FIGS. 31 to 34, a description will be given of amethod of manufacturing the objective-lens driving device 410 in thisembodiment.

First, as shown in FIG. 31, the printed circuit board 415 and the yokebase 415 formed by press working are disposed in a predeterminedposition in an unillustrated mold for injection molding, and arepositioned. Through this positioning, the printed circuit board 413 isplaced on the placing portion 415 b of the yoke base 415, and theprinted circuit board 413 is held in an upright position by using abottom 415 d of the yoke base 415 as a reference plane by means of theunillustrated mold.

In this state, the intermediate member 416 is molded by injectionmolding, as shown in FIG. 32. Since the injection molding member for theintermediate member 416 passes through the through holes 415 c providedin the yoke base 415 and the through holes 413 a provided in the printedcircuit board 413, and flows around to the opposite side, the printedcircuit board 413 and the yoke base 415 are secured firmly to theintermediate member 416. In addition, when the intermediate member 416is formed by injection molding, the guide holes 416 a and thedamping-member accommodating portion 416 b are also formed. A plan viewin this state is shown in FIG. 33, and a cross-sectional view takenalong the line C—C in FIG. 33 is shown in FIG. 34.

Next, the four wires 414 are passed through the guide holes 416 a formedin the intermediate member 416, and are connected to the soldered landportions formed on the outer surface 413 b of the printed circuit board413 by means of solder 417. The movable section 412 including theobjective lens 411 and the unillustrated coils is secured to the distalends of the wires 414 by means of soldering.

Subsequently, the damping member 418 is filled in the damping-memberaccommodating portion 416 b formed in the intermediate member 416.

The yoke base 415, the intermediate member 416, and the printed circuitboard 413 are assembled in the above-described manner.

According to this embodiment, since the yoke base 415 and the printedcircuit board 413 are simultaneously secured when the intermediatemember 416 is formed by injection molding, instead of securing the yokebase 415 and the intermediate member 416 as well as the intermediatemember 416 and the printed circuit board 413 by means of an adhesive,screws, or the like, there is an advantage in that the number ofcomponent parts and auxiliary materials used decreases, and the numberof assembling steps can also be reduced.

In addition, since the yoke base 415 and the printed circuit board 413are positioned in the mold and are integrally formed by using theintermediate member 416, the relative positional accuracy becomes high.

Also, since the molding is effected by causing the intermediate member416 to enter the through holes 413 a of the printed circuit board 413,there is no lifting off of the printed circuit board 413 at the boundarybetween the intermediate member 416 and the through holes 413 a in theprinted circuit board 413 due to temperature changes, aged deteriorationand the like. Hence, there is an advantage in that it is possible toprevent a change in the angle of the optical axis of the objective lens411 and the occurrence of unwanted resonance due to the deterioration ofthe supporting balance.

Further, if the intermediate member 416 is formed by a color whicheasily reflects light, when the wires on the printed circuit board 413are soldered by a noncontact soldering apparatus using a light beam, thelight can be focused on the soldering land portions around them withoutbeing concentrated on the through holes 413 a in the printed circuitboard 413. Hence, there is an advantage in that wire soldering can beprovided effectively.

Furthermore, since the vibration of the wires 414 is suppressed by thedamping member 418 to dampen the unwanted resonance of the movablesection 412, it becomes possible to drive the objective lens 411 moreaccurately.

It should be noted that the present invention is not limited to theabove-described embodiment, and various modifications are possible. Forinstance, the printed circuit board 413 and the yoke base 415 many notcontact each other insofar as relative positional accuracy can beensured. Also, the damping member 418 may be provided on the distal endside of the wires 414 to suppress the vibration. In addition, themovable section may be supported on both sides by means of wires. Inthis case, it suffices if the printed circuit board is disposed on atleast one fixed end side of the wires.

In accordance with the fourth embodiment of the present inventiondetailed above, the following advantages are obtained.

Since the bonding process and the screw-tightening process can beomitted in assembling the printed circuit board, the base, and theintermediate member, and the relative positional accuracy between theprinted circuit board and the base can be improved, it is possible toprovide an objective-lens driving device which facilitates fabrication,and in which the objective lens can be driven with high accuracy.

Since part of the intermediate member enters the through holes at thetime of molding the intermediate member, the joining force between theprinted circuit board and the base is strengthened, thereby improvingthe reliability.

Since the printed circuit board can be prevented from becoming liftedoff in the vicinities of the fixed ends of the resiliently supportingmembers, it is possible to prevent changes in the angle of the opticalaxis of the objective lens and the occurrence of unwanted resonance dueto the deterioration of the supporting balance.

Since the unwanted resonance of the movable section is dampened bysuppressing the vibration of the resiliently supporting members by meansof the damping member, the objective lens can be driven with greateraccuracy.

Since the base is formed integrally with the yoke, the base can befabricated easily.

What is claimed is:
 1. An optical pickup device comprising: anobjective-lens driving device for driving an objective lens, whichincludes a magnetic circuit; an optical system for transmitting andreceiving light to and from said objective lens; and a base having athrough hole formed therein, on which said objective-lens driving deviceand said optical system are mounted, and wherein at least a portion ofsaid magnetic circuit of said objective-lens driving device isaccommodated in said through hole.
 2. An optical pickup device asclaimed in claim 1, further comprising a movable plate integrally formedwith a yoke as said magnetic circuit, said yoke having a substantiallyU-shaped cross-section, on which said objective-lens driving device ismounted.
 3. An optical pickup device as claimed in claim 2, wherein aninclination of said movable plate is adjusted relative to said base.